The present invention relates to a device for reducing wear between relatively movable parts within the combustion chamber assembly of an aircraft engine and for promoting improved fuel consumption for the engine. More particularly, the subject invention relates to a self-aligning fuel nozzle assembly having multiple degrees of freedom so as to maintain the alignment of the swirler and the fuel nozzle, while accommodating any relative displacements of the combustor liner, which contains the swirler, with respect to a combustor housing to which the fuel nozzle is fixedly secured.
A gas turbine engine is essentially designed for the sole purpose of producing high velocity gases at a jet nozzle. These high velocity gases are produced in the engine by the ignition of a mixture of compressed air and fuel. The combustion of the fuel air mixture occurs within the combustion chamber assembly of the engine which basically includes a combustor housing and a thin metallic combustor liner disposed within the combustor housing and mounted thereto at one end in cantilevered fashion. The combustor liner includes an internal combustion chamber in which ignition of the compressed air and fuel takes place. The resulting post-combustion gases are expelled from the combustion chamber assembly, pass through the turbine, and are thence propelled through the jet nozzle to the atmosphere.
The burner section of the engine should be designed so that combustion efficiency is maintained at a high level. More particularly, there should be no tendency for the engine to burn out, nor should burning occur after the gases leave the outlet, i.e., complete combustion should occur entirely within the burner section. Presently known methods for promoting complete combustion include introducing fuel into the airstream as it enters the combustion chamber by means of the fuel nozzle. The fuel nozzle employs a pressure atomizing principle to aspirate the fuel in a manner providing a uniform distribution of fine particles of fuel. Fuel in this form is suitable for rapid mixing with the incoming air for combustion. Often a swirler is used in conjunction with the nozzle to more evenly distribute large quantities of the fuel-air mixture within the combustion chamber to promote rapid burning. In these prior art burner sections, the fuel nozzle is fixedly mounted to the combustor housing and extends through the swirler which is fixedly mounted to the combustor liner.
A problem with prior art swirler and fuel nozzle devices arises because typical burner sections are subject to rather extreme forces due to thermal displacements during operation of the engine. For example, the heat released per cubic foot of combustion space in the large turbojet engine is several thousand times as great as the heat released per cubic foot of burner space in an ordinary home-heating burner. At the same time, however, the burner section of the turbojet engine is also designed to deliver post combustion gases to the turbine at a temperature which does not exceed allowable limits. In most burner sections this is accomplished because only a small portion of the air entering the combustor housing from the compressor flows into the combustion chamber for ignition with the fuel, while a greater portion forms a cooling residual air flow at the outside of the combustor liner which tends to reduce the overall temperature of the total gases passing through the section. Large amounts of heat are released from the combustor liner to the residual air flow passing through the combustor housing, so that large thermal gradients are generated in the engine during use. In addition, the pressure within a 10,000 pound-thrust turbojet combustion chamber, which is enclosed by only a relatively thin thickness of steel wall, is approximately ten times as great as the pressure within the average industrial burner which is enclosed by very thick walls of fire brick and other materials. Further, very large noise levels are produced by the propulsion of large amounts of high velocity gases out of the jet nozzle. The latter, plus the movement of both the compressor and turbine vanes act to produce extensive vibrational effects throughout the engine. The thermal gradients, internal pressures, and vibrational forces act upon the various components within the burner section in a manner to cause displacements in their relative positions. Particularly troublesome is the fact that the thin steel wall combustor liner is very susceptible to these forces and as a result frequent displacements of the liner with respect to the combustor housing are experienced in normal operation of the engine.
In prior art burner sections, when the combustor liner moves the swirler moves. However, the fuel nozzle extending within the swirler remains stationary, resisting the movement of the swirler, so that movement of the liner causes wear in both the swirler and the fuel nozzle parts. When the fuel nozzle is damaged, fuel tends to be splattered into the combustion chamber rather than being sprayed therein in uniform droplets, thereby decreasing the uniform mixing of fuel and air, and thus inhibiting complete combustion. In prior art aircraft engines, it has been known to provide a swirler with an interior having a series of ridges. The frequent displacement of the combustor liner causes the ridges to act as a knife against the fuel nozzle and in some cases to actually shear off the spray end of the nozzle. When wearing and damage occurs in the swirler, the fuel mixture entering the chamber is less enriched with air and less evenly distributed throughout the chamber, also leading to retarded or incomplete combustion. Also observed, is the fact that sometimes the combustor liner moves away from the fuel nozzle thereby partially dislodging it from the swirler. A problem arises if the liner then moves towards the nozzle again at an angle. The latter motion could jam the nozzle within the swirler in a misaligned position, leading to a permanent displacement of the liner relative to the combustor housing. In this instance, the combustion efficiency of the engine is reduced because the air enrichment of the fuel reaching the combustor chamber is poor and large amounts of fuel are misdirected and remain unburned.
Accordingly, in order to overcome the shortcomings of prior art devices, it is an object of the subject invention to provide a device for maintaining the proper alignment of the swirler and fuel nozzle for any displacement of the combustor liner relative to the combustor housing during operation of the aircraft engine.
It is another object of the subject invention to provide a device for reducing wear of the swirler and the fuel nozzle parts during operation of the engine.
It is a further object of the subject invention to improve the fuel efficiency of an aircraft engine by providing a self-aligning fuel nozzle assembly capable of compensating for relative movement between a liner and a combustor housing in six degrees of freedom.